1. Field of the Invention
This invention relates to an electromagnetic force valve driving apparatus which opens and closes the suction/exhaust valve of an engine by an electromagnetic force produced by an electromagnet.
2. Description of the Prior Art
In an ordinary engine, a valve is controlled to open and close so that a cylinder may perform a suction/exhaust operation.
In one example of a drive apparatus for opening and closing such a suction/exhaust valve, a cam shaft, which is obtained by disposing cams for suction and exhaust on one shaft, is provided on the upper portion of the engine or on one side face thereof. A crankshaft, which is the rotary shaft of the engine, and the cam shaft are connected by rotary transmission means such as a belt, and the cam shaft is driven rotatively in synchronism with the rotational phase of the engine. The axial end face of the valve is pushed by the cam face of the cam shaft via a link mechanism such as a rocker arm or pushing rod. The suction/exhaust valve normally is held in the closed state by a spring and its axial end face is opened by being pushed.
In another example of a drive apparatus for opening and closing a suction/exhaust valve, a suction cam shaft having a suction cam and an exhaust cam shaft having an exhaust cam are disposed on the upper portion of an engine, the cam face of the suction cam shaft pushes the axial end face of the suction valve directly, and the cam face of the exhaust cam shaft pushes the axial end face of the exhaust valve directly, thereby opening the suction/exhaust valve.
This conventional drive apparatus for opening and closing the suction/exhaust valve results in a large-size engine because the cam shaft and link mechanism must be added onto the engine. Furthermore, since the cam shaft and link mechanism are driven by the output shaft of the engine, some of the engine output is consumed by frictional resistance when the cam shaft and link mechanism are driven. This diminishes the effective output of the engine.
Further, the actuation timing of the suction/discharge valve cannot be altered during engine operation. Since the valve actuation timing is adjusted so as to attain high efficiency in a case where the engine is running at a prescribed rpm, engine efficiency declines when it is running at an rpm different from the prescribed rpm.
In order to solve the foregoing problems, an apparatus for driving a suction/exhaust valve to open and close the same by electromagnetic force from an electromagnet, without relying upon a cam shaft, has been disclosed in Japanese Patent Application Laid-Open (KOKAI) Nos. 58-183805 and 61-76713.
However, these two publications do not disclose current control for suitably regulating electromagnetic force to the required magnitude in cases where a large current must be supplied to the electromagnet, as when the suction/exhaust valve starts to be moved in the opening direction and when it is decelerated just before being seated. Consequently, it is not possible to generate a sufficiently large electromagnetic force needed to smoothly start and decelerate the valve.